Lava Lamp: Wax-Liquid Density Crossover (2D)

What is a Lava Lamp?

A lava lamp is an iconic piece of home decor that demonstrates principles of fluid dynamics and thermodynamics. It consists of a pool of liquid (often a mixture of water and paraffin wax) in which the wax can float or sink depending on its density relative to the surrounding liquid.

The key component is the temperature difference between the upper and lower parts of the lamp, which causes the wax to change state from solid to liquid and back again.

Differential Thermal Expansion

When a substance is heated, it expands. This principle applies to both the wax and the carrier liquid in a lava lamp. However, they expand at different rates due to their distinct material properties.

The wax has a higher thermal expansion coefficient than the carrier liquid, meaning that as the temperature increases, the wax expands more rapidly.

Density Crossover

As the wax is heated and expands, its density decreases. Conversely, when it cools and contracts, its density increases.

At a specific temperature, known as the crossover point, the densities of the wax and carrier liquid become equal. This is a critical moment in the lava lamp's operation.

Stokes-Drag Motion

When the wax blobs are heated and rise to the top of the lamp, they encounter resistance from the surrounding cooler liquid due to Stokes-drag.

This drag force is proportional to the viscosity of the fluid and the velocity of the wax blob. As a result, the wax blobs move in a characteristic slow, smooth motion.

Frequently asked questions

Try it live

Everything above runs in your browser — open Lava Lamp: Wax-Liquid Density Crossover (2D) and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.